This invention relates generally to the field of variable geometry turbochargers and, more particularly, to an improved vane design for vanes for a plurality of pinioning aerodynamic vanes that are disposed within a variable geometry turbocharger for purposes of maximizing flow efficiency within the turbocharger.
Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft and housed in a compressor housing. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the turbine housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
In a turbocharger it is often desirable to control the flow of exhaust gas to the turbine to improve the efficiency or operational range of the turbocharger. Variable geometry turbochargers (VGTs) have been configured to address this need. A type of such VGT is one having a variable exhaust nozzle, referred to as a variable nozzle turbocharger. Different configurations of variable nozzles have been employed in variable nozzle turbochargers to control the exhaust gas flow. One approach taken to achieve exhaust gas flow control in such VGTs involves the use of multiple pivoting vanes that are positioned annularly around the turbine inlet. The pivoting vanes are commonly controlled to alter the throat area of the passages between the vanes, thereby functioning to control the exhaust gas flow into the turbine.
In order to ensure the proper and reliable operation of such VGTs, it is important that the individual vanes be configured and assembled within the turbine housing to move or pivot freely in response to a desired exhaust gas flow control actuation. Because these pivoting vanes are subjected to millions of high temperature cycles during turbocharger operation it is necessary that any such pivoting mechanism be one that is capable of repeatably functioning under such cycled temperature conditions without enduring any cycled temperature related material or mechanical problem or failure.
Known multiple vane VGTs include vanes that are each configured having a shaft projecting outwardly therefrom, each such shafted being positioned within a respective shaft opening in a turbine housing or nozzle wall. While the vanes are commonly actuated to pivot vis-a-vis their shafts within the respective openings, it has been discovered that such vane attachment and pivoting mechanism is not without its problems.
For example, in order to ensure freely pivoting movement of the vane shaft with the opening it is essential that the shaft project perfectly perpendicularly from the vane, to thereby avoid undesired binding or otherwise impairment of the vane pivoting movement. Secondary straightening or machining operations are sometimes necessary to ensure the perpendicularity of the vane shafts, which secondary operations can be both time consuming and costly. Additionally, this type of vane attachment and pivoting mechanism can produce a high cantilevered load on the vane shaft when actuated that can also impair free vane pivoting movement, and that can ultimately result in a vane material or mechanical failure.
An example of such a VGT is one comprising a moveable unison ring disposed within a turbocharger housing of the turbocharger, and a plurality of vanes rotatable disposed within the housing and coupled to the unison ring. The plurality of vanes are interposed within the turbine housing between an exhaust gas inlet and a turbine wheel. The unison ring is operated to rotate the vanes in unison from a closed position (restricting passage of exhaust gas to the turbine wheel) to an open position (enabling passage of exhaust gas to the turbine wheel) for purposes of controlling the turbocharger to perform in a manner that helps to optimizes air flow to the engine. An example of such a VGT is disclosed in U.S. Pat. No. 6,269,642, which is incorporated herein by reference.
Vanes used in such known VGTs are characterized as having a xe2x80x9cslimxe2x80x9d aerodynamic vane shape, i.e., having a thin airfoil or radial thickness (that is defined at its thickest region between a vane outer surface and a vane inner surface). Generally speaking a conventional vane has an airfoil thickness that is less than about 0.14, and that can be in the range of from about 0.05 to 0.14 the length of the vane (as measured between vane leading and trailing edges). While such conventional slim or thin airfoil vanes are useful for providing peak aerodynamic efficiency in a VGT, this particular vane design limits the flow turndown ratio and turbine efficiency throughout the range of motion for the vanes within the turbocharger.
It is, therefore, desirable that a vane pivoting mechanism be constructed, for use with a variable nozzle turbocharger, in a manner that provides improved vane operational reliability when compared to conventional vane pivoting mechanisms. It is also desired that an improved vane configuration be constructed that provides a throat area that is similar or better than that of the conventional slim airfoil vane configuration, while at the same time provide a throat area turndown ratio that is improved, and an improved turbine efficiency throughout the range of vane movement, when compared to the conventional slim airfoil vane configuration.
Improved vanes of this invention are constructed for use within a VGT. The VGT comprises a turbine housing having an exhaust gas inlet and an outlet, a volute connected to the inlet, and a nozzle wall adjacent the volute. A turbine wheel is carried within the turbine housing and is attached to a shaft. A plurality of such improved vanes are disposed within the turbine housing between the exhaust gas inlet and turbine wheel.
Each improved vane comprises an inner airfoil surface oriented adjacent the turbine wheel, And an outer airfoil surface oriented opposite the inner airfoil surface. The inner and outer airfoil surfaces define a vane airfoil thickness. A vane leading edge or nose is positioned along a first inner and outer airfoil surface junction, and a vane trailing edge positioned along a second inner and outer surface junction. Each vane includes a hole disposed within a first axial vane surface substantially parallel to outer nozzle wall for receiving a respective post therein that projects outwardly from the nozzle wall. Each vane also includes an actuation tab that extends from a second axial vane surface opposite from the first vane surface.
A key feature of improved vanes of this invention is that they have an airfoil thickness that is greater than conventional xe2x80x9cslimxe2x80x9d vanes. In an example embodiment, improved vanes of this invention have an airfoil thickness that is greater than about 0.16 times a length of the vane as measured between the vane leading and trailing edges. Additionally, an embodiment of the improved vane of this invention can have a complex shaped inner surface comprising a convex portion adjacent the vane leading edge, and a concave portion adjacent the vane trailing edge.